In recent years, many agents with adjuvant activity, used to specifically augment antigenspecific immune responses, have been identified. It is unclear how this diverse array of compounds enhances the adaptive immune response and what, if any, fundamental activities they have in common. In recent years it became apparent that many immunogenic agents trigger two strong pro-inflammatory signals: (i) necrotic release of cellular factors (cell death), and (ii) activation of Nod-like receptors (NLRs). The contribution of these pro-inflammatory signals, however, is unclear and the focus of this proposal. Recent studies by others and our group suggest that cathepsins control adjuvant-mediated cell death and NLR signaling. Using macrophages lacking specific cathepsins, we identified cathepsins B and S as critical for cell death mediated by alum, the most widely used adjuvant. We demonstrated that alum triggers lysosome rupture and lysosomal release of cathepsins. We used the dipeptide Leu-Leu-OMe (LL) as a model system for lysosome-disrupting agents, and found that LL triggers cathepsin C-dependent cell death, and also exhibits adjuvant activity. Based on our preliminary data we hypothesize that specific cathepsins are critical pro-inflammatory processes. Our initial goal is to identify cathepsins that are required for cell death and NLR signaling mediated by a range of prototypical adjuvants. Our ultimate goal is to determine the contribution of cell death and NLR signaling to adjuvant activities. To accomplish this objective we will specifically block these pro-inflammatory signals by using pharmacology, and mice lacking the specific cathepsins or NLR signaling components. To accomplish our objectives we propose the following three specific aims: To determine general features of cathepsin-mediated cell death, we will identify cathepsins controlling cell death induced by a range of immunogenic agents including silica, high molecular weight polyethylene and amyloid-&#946;using cathepsin-deficient macrophages. To identify specific cathepsins that control adjuvant-mediated NLR signaling, we will use a genetic approach with cathepsin-deficient macrophages. We will then block adjuvant-mediated NLR activation using mice lacking specific cathepsins and NLR components and test the impact on adjuvant activities. Recent studies suggest that adjuvanttreated macrophages release pro-inflammatory danger signals such as uric acid, endogenous papain-family proteases and ATP. Here we will test whether and to what extent these factors contribute to adjuvant activities. We predict that we will be able to control adjuvant-mediated NLR signaling and cytopathic effects using cathepsin and NLR-deficient mice. An understanding of critical host responses mediated by adjuvants will fundamentally improve the rational design of adjuvants in terms of both the strength and specificity of the desired immune response.